In order to improve the temperature resistance and salt tolerance as well as environmental performance of water-based drilling fluid viscosity enhancer，and meet the needs of shale oil drilling construction，viscosity enhancer HBZ-2 was prepared using methacrylamide （MAA），N-vinyl pyrrolidone （NVP） and polymerizable quaternary ammonium salt cationic monomer （H-12）as raw materials. The molecular structure of HBZ-2 was characterized by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy，and then its mechanism of action was analyzed. The thickening performance，temperature resistance，salt tolerance and environmental performance of HBZ-2，and the basic properties of drilling fluid were investigated. The results showed that under the same experimental conditions，the thickening performance，temperature resistance and salt tolerance of HBZ-2 were superior to those of the same type of viscosity enhancer HE300 and 80A51. When the dosage of HBZ-2 was 1%，the apparent viscosity of seawater based slurry could be increased from 10.5 mPa·s to 54.5 mPa·s. After high-temperature aging at 200 ℃，the viscosity of seawater based slurry containing 20% sodium chloride or 5% calcium chloride could still reach over 30 mPa·s，indicating strong temperature resistance and salt tolerance. The basic properties of drilling fluid system containing 1%HBZ-2 after high-temperature aging were relatively stable，with a shale rolling recovery rate of over 90% and a temperature resistance of up to 200 ℃. HBZ-2 and drilling fluid system had low biological toxicity and good biodegradability，with EC50 value of 204 400 mg/L and 120 500 mg/L，respectively，and BOD5/COD value of 40.9% and 33.6%，respectively. In addition，HBZ-2 did not contain heavy metals，while the content of some heavy metals in drilling fluid system was also much lower than that of the relevant industry standards， indicating excellent environmental performance. The viscosity enhancer HBZ-2 had excellent performance and was suitable for offshore shale oil drilling with high environmental performance requirements.